[RFC PATCH v1 6/8] selftests/nolibc: Add `sigaction(2)` selftest

[Ammar Faizi <ammarfaizi2@gnuweeb.org>]

From: Ammar Faizi <ammarfaizi2@gnuweeb.org>

Test the sigaction() function implementation. Test steps:

 - Set a signal handler.
 - Then send a signal to itself using the kill() syscall.
 - The program has to survive and store the caught signal number in a
   volatile global variable.
 - Validate the volatile global variable value.
 - Restore the original signal handler.

Only the x86-64 arch runs this test. Other architectures skip this test
for now.

Signed-off-by: Ammar Faizi <ammarfaizi2@gnuweeb.org>
---
 tools/testing/selftests/nolibc/nolibc-test.c | 81 ++++++++++++++++++++
 1 file changed, 81 insertions(+)

diff --git a/tools/testing/selftests/nolibc/nolibc-test.c b/tools/testing/selftests/nolibc/nolibc-test.c
index 309cabbddeec..562766e0f63c 100644
--- a/tools/testing/selftests/nolibc/nolibc-test.c
+++ b/tools/testing/selftests/nolibc/nolibc-test.c
@@ -486,6 +486,86 @@ static int test_fork(void)
 	return 0;
 }
 
+static volatile int g_test_sig;
+
+static void test_sigaction_signal_handler(int sig)
+{
+	g_test_sig = sig;
+}
+
+static int test_sigaction_sig(int sig)
+{
+	const struct sigaction new = {
+		.sa_handler = test_sigaction_signal_handler
+	};
+	struct sigaction old;
+	int ret;
+
+	/*
+	 * Set the signal handler.
+	 */
+	ret = sigaction(sig, &new, &old);
+	if (ret) {
+		printf("test_sigaction_sig(%d): Failed to set a signal handler\n", sig);
+		return ret;
+	}
+
+	/*
+	 * Test the signal handler.
+	 */
+	g_test_sig = 0;
+	kill(getpid(), sig);
+
+	/*
+	 * test_sigaction_signal_handler() must set @g_test_sig to @sig.
+	 */
+	if (g_test_sig != sig) {
+		printf("test_sigaction_sig(%d): Invalid g_test_sig value (%d != %d)\n", sig, g_test_sig, sig);
+		return -1;
+	}
+
+	/*
+	 * Restore the original signal handler.
+	 */
+	ret = sigaction(sig, &old, NULL);
+	if (ret) {
+		printf("test_sigaction_sig(%d): Failed to restore the signal handler\n", sig);
+		return ret;
+	}
+
+	return 0;
+}
+
+static int test_sigaction(void)
+{
+	static const int sig_to_test[] = {
+		SIGINT,
+		SIGHUP,
+		SIGTERM,
+		SIGQUIT,
+		SIGSEGV
+	};
+	size_t i;
+	int ret;
+
+	for (i = 0; i < (sizeof(sig_to_test) / sizeof(sig_to_test[0])); i++) {
+		ret = test_sigaction_sig(sig_to_test[i]);
+		if (ret)
+			return ret;
+	}
+
+	return 0;
+}
+
+static int should_test_sigaction(void)
+{
+#if defined(__x86_64__)
+	return 1;
+#else
+	return 0;
+#endif
+}
+
 /* Run syscall tests between IDs <min> and <max>.
  * Return 0 on success, non-zero on failure.
  */
@@ -566,6 +646,7 @@ int run_syscall(int min, int max)
 		CASE_TEST(select_null);       EXPECT_SYSZR(1, ({ struct timeval tv = { 0 }; select(0, NULL, NULL, NULL, &tv); })); break;
 		CASE_TEST(select_stdout);     EXPECT_SYSNE(1, ({ fd_set fds; FD_ZERO(&fds); FD_SET(1, &fds); select(2, NULL, &fds, NULL, NULL); }), -1); break;
 		CASE_TEST(select_fault);      EXPECT_SYSER(1, select(1, (void *)1, NULL, NULL, 0), -1, EFAULT); break;
+		CASE_TEST(sigaction);         EXPECT_SYSZR(should_test_sigaction(), test_sigaction()); break;
 		CASE_TEST(stat_blah);         EXPECT_SYSER(1, stat("/proc/self/blah", &stat_buf), -1, ENOENT); break;
 		CASE_TEST(stat_fault);        EXPECT_SYSER(1, stat(NULL, &stat_buf), -1, EFAULT); break;
 		CASE_TEST(symlink_root);      EXPECT_SYSER(1, symlink("/", "/"), -1, EEXIST); break;
-- 
Ammar Faizi